1. Field of the Invention:
The invention relates to the art of refrigerant expansion valves.
2. Description of the Prior Art:
One commonly used automatic expansion valve for controlling the flow of refrigerant between a condenser and an evaporator is called a constant pressure refrigerant expansion valve and is designed to attempt to keep a constant absolute pressure in the evaporator during operation of the system. This valve is typically operated by a preset spring force and a force derived from the feedback of the pressure from the evaporator. The valve is arranged so that with the valve set and feeding refrigerant at a given pressure, a small increase in the evaporator pressure will act to move the valve toward a closing direction, thereby restricting the refrigerant flow and limiting the evaporator pressure. When the evaporator pressure drops below the valve setting because of a decrease in load, the valve moves in an opening position to increase the refrigerant flow in an effort to raise the evaporator pressure to the particular balanced valve setting. In a number of applications of the valve, including some room air conditioners, the valve is provided with a bypass in the form of a small slot or drilled hole in the valve seat or valve pin to prevent complete valve close-off when the compressor shuts down. This is to permit refrigerant to continue to flow at a reduced rate until high and low side pressures are equalized.
While the bypass type valve provides for the equalization after several minutes, it is believed that the bypass itself contributes to a problem which occurs when an air conditioner is operated without any forced air flow over the evaporator and compressor. In such an arrangement using a constant pressure bypass type valve, and starting with the system pressures equalized, but with the fans not operating, the valve remains closed and gives a bypass feed only. If this occurs in a system using an expansion valve which also includes a relief valve, and with, say, R-22 refrigerant, the relief valve will open at say a 600-700 p.s.i. differential so that refrigerant can then flow to the compressor and load it sufficiently that the current and temperature overload means will be operated to shut the compressor down. However if the expansion valve does not include the relief valve, the condenser pressure can build up to a value of up to 200 p.s.i. over what would be desirable before the current and temperature overload of the compressor operates. It is believed that if the bypass in the expansion valve were omitted, it is likely that the high pressure problem would be avoided. However this would not permit equalization of the system after shutdown.
The valve according to the invention is considered to be preferable in that no bypass arrangement is needed for equalization, and under a fan failure condition the valve functions in a manner which does not create any problems for the air conditioning system itself.
Of the prior art patents of which applicant is aware, U.S. Pat. No. 1,786,110 is considered to be the closest in the field of refrigerant expansion valves, but differs substantially in that it in effect includes two valves, one of which functions as an on-off valve, while the other functions like a capillary tube; neither of which corresponds to the operation of the valve of applicant's invention.
Flow control devices for controlling the flow of lubricant to hydrostatic bearings and similar in structure to the valve arrangements embodying this invention are disclosed in U.S. Pat. No. 3,110,527. However, these devices are incorporated in a system where an increase in differential pressure between a source pressure and the load pressure is taught to result in a restriction of the flow, which would be directly the opposite of the result of the operation of the refrigerant expansion valve of this invention.